1. Field of the Invention
This invention relates to a fully-automatic driving device for a power-driven antenna of a radio for use in a vehicle.
2. Description of the Prior Art
A system for automatically extending and retracting an antenna arranged on a vehicle body for a radio in a vehicle has been known as shown in FIG. 1.
With this arrangement, when an ignition switch 1 is turned on and a radio switch 2 of a lock type is then switched on, a current is supplied from a battery 3 through these switches 1 and 2 to a radio 4 to actuate it and simultaneously a current is supplied to an exciting coil 5a of a relay 5 in the same manner to close a normally opened contact 5b. At this moment, an antenna rod has been retracted and hence a limit switch 6 has been closed to the on state so that a driving current flows from the battery 3 between terminals 7a and 7c of a motor 7 through the switches 1 and 2, contact 5b and the limit switch 6 to extend the antenna rod.
When the antenna rod extends to a predetermined length, the limit switch 6 is opened or turned off to shut off the driving current for the motor 7 so as to stop the extension of the antenna rod.
With the radio 4 in the operative condition and the extended antenna rod, when the ignition switch 1 or the radio switch 2 is turned off, the current supply to the radio 4 and the exciting coil 5a of the relay 5 is shut off to turn off the radio 4 and simultaneously to close a normally closed contact 5c. At this moment, the antenna rod has extended and hence a limit switch 8 has been closed to an on state, so that the current flows from the battery 3 between terminals 7b and 7c of the motor 7 through the contact 5c and the switch 8 now to retract the antenna rod.
When the antenna rod has been retracted to a predetermined length and housed in the body, the limit switch 8 is opened to shut off the driving current for the motor 7 so as to stop the retraction of the antenna rod.
With the driving device of the prior art as described with reference to FIG. 1, the antenna rod is adapted to extend or retract automatically in response to the on and off of the ignition switch 1 and radio switch 2. With such a driving device, the ignition switch is often turned off to stop an engine without switching off the radio switch 2. In this case, the antenna rod will extend at the moment when the ignition switch is again turned on for starting the engine, because of the lock type radio switch 2 remaining in an on condition. If a driver is not aware of the extension of the antenna, there is a danger to a person near the antenna and a risk of a touch of the antenna with a shutter of a garage when a car is being driven into or out of the garage.